The development of the incandescent bulb and the electrochemical cell has led to the development of the flashlight and similar portable light systems based on the incandescent bulb. Such flashlights, however, are not wholly satisfactory and even with all of the improvements made over the years the incandescent lamp flashlight still has inherent problems.
The flashlight is an inefficient light source due to the very low efficiency of the incandescent lamp in converting electrical energy into visible light. Much of the electrical energy consumed by the incandescent lamp is converted into heat, which is dissipated into the environment without serving any useful function. The low efficiency of the incandescent lamp has usually required the lamp to be used with a parabolic or similar reflector. Further, the incandescent lamp employs a filament which produces a point source of light, the reflector concentrates this point source of light into a narrow beam producing an uneven spot type illumination.
With the invention of the fluorescent lamp an alternative light source became available. The fluorescent lamp is much more efficient in converting electrical energy into visible light than is an incandescent lamp. This high efficiency makes the fluorescent lamp an ideal replacement for the incandescent lamp in many applications. The higher efficiency of the fluorescent lamp is particularly attractive for portable light uses, where the amount of electrical energy available is fixed and limited to that contained in the batteries present within the lantern.
A fluorescent lamp generates light on the inner surface of the lamp envelope. This produces a much more diffuse light than the point source generated by the incandescent lamp. The diffuse light, coupled with the larger amount of light available, permits the lamp to be used with a flat reflector. This produces a more even illumination over a much larger area than the small uneven spot produced by an incandescent lamp.
A fluorescent lamp requires a ballast circuit and a supply of alternating current at a high frequency and at a much higher voltage than the direct current required by the incandescent lamp. This higher voltage in portable fluorescent lanterns is supplied by a self-contained power source, usually an inverter-ballast circuit powered by batteries. The efficiency of this circuit in converting the direct current supplied by the batteries into the high alternating current voltage required by the fluorescent lamp determines the amount of light and the total number of hours of light obtained from a given set of batteries and fluorescent lamp. The higher the efficiency of the inverter-ballast circuit the more hours of light will be obtained from a given set of batteries.
The higher voltage required by a fluorescent lamp causes difficulties in the design of the lantern case. One such difficulty is that the high voltage, after being produced, must be channeled to the lamp without being reduced or permitted to leak out of the case. Leakage reduces the efficiency of the lantern. No such potential problems existed with incandescent lamps because of the low direct current associated with those lamps.
The high voltage lamp requires several batteries in series to supply the voltage and current needed by the inverter-ballast circuit to properly operate the fluorescent lamp. The large number of batteries in turn dictates a case that will not be damaged by impact, which would be accentuated by the increased number of batteries required.
The previously recited problems can be further compounded by when and how the portable fluorescent lantern is used. Portable lanterns are usually used outside of the controlled environment of the home or office. Fluorescent lanterns will usually be found in backyards, on campgrounds and on boats. The high humidity found in all these environments increases the likelihood of voltage leakage. Battery contact corrosion accelerated by high humidity reduces the voltage at the inverter-ballast input. The presence of bodies of water or rain in areas of lantern use, creates the possibility of lantern failure on lantern submersion or penetration by water. These events usually occur at a time when the lantern is most needed, as in a storm.
The entry of water, especially salt water even in very small quantities, is detrimental to conventional portable fluorescent lanterns. Water actively promotes corrosion within the lantern, which increases the resistance of all electrical contacts, resulting in decreased light output and eventual lantern failure. Further, water provides a leakage path for the alternating current voltage produced within the lantern. This also reduces the voltage reaching the lamp and reduces the light output and efficiency of the lantern. Corrosion and leakage paths are of especial concern in the area of the inverter-ballast circuit. The various components of the inverter-ballast circuit are very close to each other, and corrosion and leakage paths will quickly cause the total failure of the circuit.
Even if no moisture enters the lantern, previously known lanterns have malfunctioned due to failure of the mechanical switches previously used. Through the abuse or, in many cases simply through their use, the mechanical switches failed or developed high resistance. This led to reduced light output and ultimately to failure of the lantern.
A further problem encountered in fluorescent light systems occurred because the fluorescent lamp acts as a load on the inverter-ballast circuit and removal of the lamp during circuit operation can cause inverter runaway and subsequent failure of the self-contained power source. For this reason, in the past, care had to be taken by the usually unaware user to make sure that the circuit was switched off or the batteries removed before the lamp was removed from the lantern.